Image sensor and image capturing device

ABSTRACT

An image sensor includes: a pixel substrate that includes a plurality of pixels each having a photoelectric conversion unit that generates an electric charge through photoelectric conversion executed on light having entered therein and an output unit that generates a signal based upon the electric charge and outputs the signal; and an arithmetic operation substrate that is laminated on the pixel substrate and includes an operation unit that generates a corrected signal by using a reset signal generated after the electric charge in the output unit is reset and a photoelectric conversion signal generated based upon an electric charge generated in the photoelectric conversion unit and executes an arithmetic operation by using corrected signals each generated in correspondence to one of the pixels.

This is a divisional of U.S. patent application Ser. No. 16/085,160filed Sep. 14, 2018, which is the U.S. National Stage of InternationalApplication No. PCT/JP2017/007549 filed Feb. 27, 2017, and which claimspriority from Japanese Application No. 2016-060001 filed in Japan onMar. 24, 2016. The disclosure of each of the prior applications isincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an image sensor and image capturingdevice.

BACKGROUND ART

There is an image sensor known in the related art that executesarithmetic operations by using signals output from adjacent pixels(PTL1). In this image sensor, no correlated double sampling (CDS) isexecuted prior to an arithmetic operation executed by using pixelsignals, and for this reason, a noise signal component originating fromeach pixel cannot be removed.

CITATION LIST Patent Literature

PTL1: Japanese Laid Open Patent Publication No. 2001-94888

SUMMARY OF INVENTION

According to the 1st aspect of the present invention, an image sensorcomprises: a pixel substrate that includes a plurality of pixels eachhaving a photoelectric conversion unit that generates an electric chargethrough photoelectric conversion executed on light having enteredtherein and an output unit that generates a signal based upon theelectric charge and outputs the signal; and an arithmetic operationsubstrate that is laminated on the pixel substrate and includes anoperation unit that generates a corrected signal by using a reset signalgenerated after the electric charge in the output unit is reset and aphotoelectric conversion signal generated based upon an electric chargegenerated in the photoelectric conversion unit and executes anarithmetic operation by using corrected signals each generated incorrespondence to one of the pixels.

According to the 2nd aspect of the present invention, an image sensorcomprises: a pixel substrate at which a plurality of pixels, each havinga photoelectric conversion unit and an output unit, are disposed; and anarithmetic operation substrate at which an operation unit that generatesa corrected signal by using a reset signal, resulting from digitalconversion of a signal generated after resetting the output unit, and aphotoelectric conversion signal, resulting from digital conversion of asignal generated through photoelectric conversion at the photoelectricconversion unit, and executes an arithmetic operation with correctedsignals, each generated in correspondence to one of the pixels, isdisposed in correspondence to each of the pixels, wherein: the pixelsubstrate and the arithmetic operation substrate are laminated one uponanother.

According to the 3rd aspect of the present invention, an image capturingdevice comprises: an image sensor according to the 1st or the 2ndaspect; and an image generation unit that generates image data basedupon signals provided from the pixels.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A block diagram illustrating the structure adopted in the imagecapturing device achieved in a first embodiment

FIG. 2 A sectional view of the structure adopted in the image sensor inthe first embodiment

FIG. 3 A block diagram illustrating the structure of the image sensorachieved in the first embodiment

FIG. 4 A circuit diagram illustrating the structure adopted in a pixelin the first embodiment

FIG. 5 A block diagram illustrating in detail the structure adopted inthe image sensor in the first embodiment

FIG. 6 A timing chart pertaining to the operation executed in the imagesensor in the first embodiment

FIG. 7 A block diagram illustrating in detail the structure adopted inan image sensor achieved as variation 1

DESCRIPTION OF EMBODIMENT First Embodiment

FIG. 1 is a block diagram illustrating the structure adopted in theimage capturing device achieved in the first embodiment. An imagecapturing device 1 includes a photographic optical system 2, an imagesensor 3 and a control unit 4. The image capturing device 1 may be, forinstance, a camera. The photographic optical system 2 forms a subjectimage on the image sensor 3. The image sensor 3 generates image signalsby capturing the subject image formed via the photographic opticalsystem 2. The image sensor 3 may be, for instance, a CMOS image sensor.The control unit 4 outputs a control signal to control an operation ofthe image sensor 3, to the image sensor 3. In addition, the control unit4 functions as an image generation unit that generates image data byexecuting various types of image processing on image signals output fromthe image sensor 3. It is to be noted that the photographic opticalsystem 2 may be a detachable system that can be mounted at or dismountedfrom the image capturing device 1.

FIG. 2 shows the structure adopted in image sensor in the firstembodiment in a sectional view. The image sensor 3 shown in FIG. 2 is abackside-illumination image sensor. The image sensor 3 includes a firstsubstrate 111, a second substrate 112, a third substrate 113 and afourth substrate 114. The first substrate 111, the second substrate 112,the third substrate 113 and the fourth substrate 114 are eachconstituted with, for instance, a semiconductor substrate. The firstsubstrate 111 is laminated on the second substrate 112, the secondsubstrate 112 is laminated on the third substrate 113 and the thirdsubstrate 113 is laminated on the fourth substrate 114. As the unfilledarrow in FIG. 7 indicates, incident light L enters the image sensor 3primarily toward the + side along a Z axis. In addition, coordinate axesare set so that the left side of the drawing sheet along an X axisrunning perpendicular to the Z axis is the X axis + side and that theside closer the viewer looking at the drawing along a Y axis runningperpendicular to both the Z axis and the X axis is the Y axis + side.

The image sensor 3 further includes a microlens layer 101, a colorfilter layer 102 and a passivation layer 103. The passivation layer 103,the color filter layer 102 and the microlens layer 101 are laminated atthe first substrate 111 in sequence. The microlens layer 101 includes aplurality of microlenses ML. A microlens ML condenses light havingentered therein onto a photoelectric conversion unit 12 to be describedlater. The color filter layer 102 includes a plurality of color filtersF. The passivation layer 103 is constituted with a nitride film or anoxide film.

The first substrate 111, the second substrate 112, the third substrate113 and the fourth substrate 114 respectively include first surfaces 105a, 106 a, 107 a and 108 a, at which gate electrodes and gate insulatingfilms are disposed, and second surfaces 105 b, 106 b, 107 b and 108 b,which are different from the first surfaces. In addition, variouselements such as transistors are disposed at the first surfaces 105 a,106 a, 107 a and 108 a. Wiring layers 140, 141, 144 and 145 arelaminated respectively on the first surface 105 a of the first substrate111, on the first surface 106 a of the second substrate 112, on thefirst surface 107 a of the third substrate 113 and on the first surface108 a of the fourth substrate 114. Furthermore, substrate connectinglayers 142 and 143 are laminated respectively on the second surface 106b of the second substrate 112 and on the second surface 107 b of thethird substrate 113. The wiring layers 140 through 145 each include aconductor film (metal film) and an insulating film, with a plurality ofwirings and vias disposed therein.

The elements disposed at the first surface 105 a of the first substrate111 and the elements disposed at the first surface 106 a of the secondsubstrate 112 are electrically connected by connecting portions 109,such as bumps or electrodes, via the wiring layers 140 and 141, and theelements disposed at the first surface 107 a of the third substrate 113and the elements disposed at the first surface 108 a of the fourthsubstrate 114 are likewise electrically connected by connecting portions109, such as bumps or electrodes, via the wiring layers 144 and 145. Inaddition, the second substrate 112 and the third substrate 113 eachinclude through holes 120 formed so as to pass from the first surfacethrough to the second surface of the substrate and a plurality ofthrough electrodes 110, such as through silicon vias, each disposed torange from the first surface through to the second surface via a throughhole 120. A through electrode 110 disposed at the second substrate 112connects a circuit disposed at the first surface 106 a with a circuitdisposed at the second surface 106 b of the second substrate 112,whereas a through electrode 110 disposed at the third substrate 113connects a circuit disposed at the first surface 107 a with a circuitdisposed at the second surface 107 b of the third substrate 113. Acircuit disposed at the second surface 106 b of the second substrate 112and a circuit disposed at the second surface 107 b of the thirdsubstrate 113 are electrically connected with each other by a connectingportion 109, such as a bump or an electrode, via the substrateconnecting layers 142 and 143.

FIG. 3 is a block diagram illustrating the structure adopted in theimage sensor in the first embodiment. The first substrate 111 includes aplurality of pixels 10 and a plurality of comparison units 40, bothdisposed in a two-dimensional pattern. The plurality of pixels 10 aredisposed both along the X axis and along the Y axis shown in FIG. 2. Thepixels 10 each output a photoelectric conversion signal and a noisesignal, which will be described later, to a comparison unit 40. Thecomparison units 40, each disposed in correspondence to one of thepixels 10, are constituted with comparator circuits or the like. Acomparison unit 40 compares the photoelectric signal and the noisesignal output from the corresponding pixel 10 individually with areference signal, and outputs comparison results to the second substrate112. The second substrate 112 includes a plurality of storage units 50.The storage units 50, each disposed in correspondence to one of thepixels 10, are constituted with latch circuits or the like. Based uponthe comparison results provided by the corresponding comparison unit 40,a count value corresponding to the length of time having elapsed sincethe start of comparison executed by the comparison unit 40 is stored asa digital signal into each storage unit 50. A digital signalcorresponding to the photoelectric conversion signal and a digitalsignal corresponding to the noise signal are stored in the storage unit50. In addition, the storage unit 50 also functions as an accumulatingunit 50 that accumulates the photoelectric conversion signal and thenoise signal (reset signal) having been converted to digital signals. Aswill be explained in detail later, the comparison unit 40 and thestorage unit 50 constitute an integrated A/D conversion unit thatconverts the photoelectric conversion signal and the noise signal todigital signals. The digital signals stored in the storage unit 50 areoutput via the third substrate 113 to the fourth substrate 114.

The fourth substrate 114 includes a plurality of ALUs (arithmetic andlogic units), i.e., arithmetic operation units 80. The arithmeticoperation units 80, each disposed in correspondence to one of the pixels10, execute signal processing, such as correlated double sampling (CDS)through subtraction using the digital signal generated based upon thephotoelectric conversion signal and the digital signal generated basedupon the noise signal, and an arithmetic operation executed by usingsignals generated in correspondence to individual pixels. The arithmeticoperation units 80 are each configured so as to include an addingcircuit, a subtracting circuit, a flip-flop circuit, a shift circuit andthe like. The various arithmetic operation units 80 are connected withone another via signal lines, switches SW and the like.

The third substrate 113 includes ALU control units 70 (hereafterreferred to as control units 70) that control the arithmetic operationunits 80. The control units 70 are each disposed in correspondence toone of the pixels 10 and each control specific details and the like ofarithmetic operations executed by the corresponding arithmetic operationunit 80 by outputting a control signal to the arithmetic operation unit80, a switch SW or the like disposed in the fourth substrate 114. Forinstance, a control unit 70 selects signals from specific pixels byexecuting ON control of specific switches SW and in response, thearithmetic operation unit 80 corresponding to the particular controlunit 70 executes arithmetic operation processing on the signals from theplurality of pixels having been selected. It is to be noted that thefirst substrate 111 is configured as a pixel substrate 111 that includesthe plurality of pixels 10 each having a photoelectric conversion unit12 and a readout unit (output unit) to be explained later, whereas thesecond substrate 112 is configured as an accumulation substrate 112 thatincludes the accumulating units 50 (storage units 50). In addition, thefourth substrate 114 is configured as an arithmetic operation substrate114 that includes the arithmetic operation units 80.

In the embodiment, correlated double sampling is executed prior to anarithmetic operation executed by using the signals provided from theindividual pixels 10. This means that an arithmetic operation can beexecuted by using the signals provided from selected pixels 10 after thenoise signal component originating in each pixel 10 is removed from thecorresponding signal. In addition, the arithmetic operation unit 80 andthe control unit 70 are laminated on the pixel 10. This makes itpossible to prevent a decrease in the opening ratio at the pixel 10.Furthermore, the control units 70 in the third substrate 113 eachcontrol the corresponding arithmetic operation unit 80 disposed in thefourth substrate 114 by providing a control signal to the arithmeticoperation unit 80 along the direction in which the Z axis extends inFIG. 2. As a result, an arithmetic operation can be executed by usingthe signals from selected pixels 10 without having to increase the chiparea in the image sensor 3.

FIG. 4 is a circuit diagram illustrating the structure adopted in apixel in the image sensor in the first embodiment. The pixels 10 eachinclude a photoelectric conversion unit 12 constituted with, forinstance, a photodiode (PD) and a readout unit 20. The photoelectricconversion unit 12 has a function of converting light having enteredtherein to an electric charge and accumulating the electric chargeresulting from the photoelectric conversion. The readout unit 20includes, for instance, a transfer unit 13, a discharge unit 14, afloating diffusion (FD) 15, an amplifier unit 16 and a current source17.

The transfer unit 13, which is controlled with a signal Vtx, transfersthe electric charge resulting from the photoelectric conversion executedat the photoelectric conversion unit 12 to the floating diffusion 15. Inother words, the transfer unit 13 forms an electric charge transfer pathbetween the photoelectric conversion unit 12 and the floating diffusion15. The electric charge is held (accumulated) at the floating diffusion15. The amplifier unit 16 amplifies a signal generated based upon theelectric charge held in the floating diffusion 15 and outputs theamplified signal to a signal line 18. In the example presented in FIG.4, the amplifier unit 16 is constituted with a transistor M3 with thedrain terminal, the gate terminal and the source terminal thereofrespectively connected to a source VDD, the floating diffusion 15 andthe current source 17.

The discharge unit (reset unit) 14, which is controlled with a signalVrst, discharges the electric charge at the floating diffusion 15,thereby resetting the potential at the floating diffusion 15 to a resetpotential (reference potential). The transfer unit 13 and the dischargeunit 14 may be constituted with, for instance, a transistor M1 and atransistor M2 respectively.

The readout unit 20 reads out, in sequence, a signal (photoelectricconversion signal) corresponding to the electric charge transferred fromthe photoelectric conversion unit 12 to the floating diffusion 15 viathe transfer unit 13 and a signal (noise signal), generated as thepotential at the floating diffusion 15 is reset to the reset potential,to the signal line 18. The readout unit 20 functions as an output unit20 that generates a signal based upon an electric charge accumulated inthe floating diffusion 15 and outputs the signal thus generated. Theoutput unit 20 outputs the photoelectric conversion signal and the noisesignal to the signal line 18.

FIG. 5 is a block diagram illustrating in detail the structure adoptedin the image sensor in the first embodiment. The image sensor includes aplurality of pixels 10, operation units 100 each disposed incorrespondence to one of the pixels 10, a timing generator 200, a D/Aconversion unit 210, a global counter 220, a shift register 230, a VSCANcircuit (vertical scanning circuit) 240, an HSCAN circuit (horizontalscanning circuit) 250, a sense amplifier 300, a line memory 310 and aninput/output unit 320. The operation units 100 each include ananalog/digital conversion unit (A/D conversion unit) 60, a control unit70, an arithmetic operation unit 80, a storage unit 83, a demultiplexer81, a demultiplexer 84 and a multiplexer 85. The A/D conversion unit 60is configured with a comparison unit 40, a storage unit 50 and ademultiplexer 83. In addition, the storage unit 50 includes a signalstorage unit 51 where a digital signal corresponding to thephotoelectric conversion signal is stored and a noise storage unit 53where a digital signal corresponding to the noise signal is stored. Thesignal storage unit 51 and the noise storage unit 52 are eachconstituted with a plurality of latch circuits corresponding to thenumber of bits in the signal stored therein. For instance, the signalstorage unit 51 and the noise storage unit 52 may each be constitutedwith 12 latch circuits and in such a case, the digital signals stored inthe signal storage unit 51 and the noise storage unit 52 are each a12-bit parallel signal.

At a first layer, i.e., the first substrate 111 in the image sensor 3,the pixels 10, the comparison units 40 and part of the timing generator200 are disposed. The timing generator 200 is configured with aplurality of circuits that are disposed at the different substrates,i.e., the first substrate 111 through the fourth substrate 114. It is tobe noted that the first substrate 111, the second substrate 112, thethird substrate 113 and the fourth substrate 114 are respectivelynotated as a first layer, a second layer, a third layer and a fourthlayer in FIG. 5. The various circuits constituting the timing generator200 are disposed at the periphery of the area where the pixels 10 andthe operation units 100 are disposed. At the second layer, i.e., thesecond substrate 112, the signal storage units 51, the noise storageunits 52, the demultiplexers 53, the D/A conversion unit 210, the globalcounter 220, the shift register 230 and part of the timing generator 200are disposed.

At the third substrate 113, the control units 70, the VSCAN circuit 240,the HSCAN circuit 250 and part of the timing generator 200 are disposed.At the fourth substrate 114, the arithmetic operation units 80, thestorage units 83, the demultiplexers 81, the demultiplexers 84, thesense amplifier 300, the line memory 310 and the input/output unit 320are disposed. In addition, the D/A conversion unit 210, the globalcounter 220, the shift register 230, the VSCAN circuit 240, the HSCANcircuit 250, the sense amplifier 300, the line memory 310 and theinput/output unit 320 are disposed at the periphery of the areas wherethe operation units 100 are present at the various substrates.

The timing generator 220, constituted with a pulse generation circuit orthe like, generates a pulse signal and the like based upon a registervalue setting output from the control unit 4 in the image capturingdevice 1 and outputs the pulse signal or the like thus generated to theindividual pixels 10, the D/A conversion unit 210, the global counter220, the shift register 230, the VSCAN circuit 240 and the HSCAN circuit250. The register value setting is selected in correspondence to, forinstance, the shutter speed (the length of time over which electriccharges are accumulated in the photoelectric conversion units), the ISOsensitivity, whether or not image correction is executed or the like.The D/A conversion unit 210 generates, based upon the pulse signalprovided from the timing generator 200, a ramp signal with a shiftingsignal level, which is to be used as a reference signal. In addition,the D/A conversion unit 210 is commonly connected to the individualcomparison units 40 each disposed in correspondence to one of the pixels10, and outputs the reference signal to the comparison units 40. Theglobal counter 220 generates a clock signal indicating a count valuebased upon the pulse signal provided from the timing generator 200, andoutputs the clock signal thus generated to the signal storage unit 51and the noise storage unit 52. The shift register 230 generates a timingsignal based upon the pulse signal provided from the timing generator200 and outputs the timing signal thus generated to the signal storageunit 51 and the noise storage unit 52.

The VSCAN circuit 240 and the HSCAN circuit 250 each sequentially selectthe individual control units 70 based upon a signal provided by thetiming generator 200 and each output a signal, indicating to eachcontrol unit 70, the details of an arithmetic operation (among the fourarithmetic operations) to be executed in the arithmetic operation unit80 and the pixels 10 and the like selected as the arithmetic operationtargets. The sense amplifier 300 is connected to a signal line 122 towhich the operation units, each disposed in correspondence to one of thepixels 10, are connected, and reads out signals at high speed byamplifying signals input to the signal line 122 and reading out theamplified signals. The signals having been read out by the senseamplifier 300 are stored in the line memory 310. The input/output unit320 executes signal processing such as signal bit-width adjustment andsynchronization code assignment for signals output from the line memory310 and outputs signals resulting from the signal processing as imagesignals to the control unit 4 of the image capturing device 1. Theinput/output unit 320 constituted with, for instance, an input/outputcircuit supporting a high-speed interface such as an LVDS or an SLVS,transmits signals at high speed.

FIG. 6 is a timing chart pertaining to an example of an operation thatmay be executed in the image sensor in the first embodiment. In FIG. 6,time points are indicated along the horizontal axis. During a timeperiod elapsing between a time point tl and a time point t2, registersetting information is input to the timing generator 200 from thecontrol unit 4 of the image capturing device 1. During a time periodelapsing between the time point t2 and a time point t3, the timinggenerator 200 generates signals indicating arithmetic operation detailsand the like for the individual arithmetic operation units 80, basedupon the register value setting information and outputs the signals thusgenerated to the VSCAN circuit 240 and the HSCAN circuit 250. During atime period elapsing between the time point t3 and a time point t4, theVSCAN circuit 240 and the HSCAN circuit 250 sequentially output thesignals indicating the arithmetic operation details or the like, whichhave been generated by the timing generator 200, to the individualcontrol units 70, each disposed in correspondence to one of the pixels10.

During a time period elapsing between a time point t10 and a time pointt11, a noise signal from each pixel 10 is output to the correspondingcomparison unit 40. The comparison unit 40 compares the noise signalread out from the pixel 10 with a reference signal provided from the D/Aconversion unit 210 and outputs comparison results to the demultiplexer53. The demultiplexer 53 outputs the comparison results provided by thecomparison unit 40 to the noise storage unit 52. A count value thatcorresponds to the length of time having elapsed between the start ofthe comparison executed by the comparison unit 40 and the output of thecomparison results, is stored as a digital signal corresponding to thenoise signal into the noise storage unit 52 based upon the comparisonresults provided by the comparison unit 40 and a clock signal providedby the global counter 220.

During a time period elapsing between the time point t11 and a timepoint t12, the photoelectric conversion signal in each pixel 10 isoutput to the corresponding comparison unit 40. The comparison unit 40compares the photoelectric conversion signal with a reference signal andoutputs comparison results to the demultiplexer 53. The demultiplexer 53outputs the comparison results provided by the comparison unit 40 to thesignal storage unit 51. A count value that corresponds to the length oftime having elapsed since the start of the comparison executed by thecomparison unit 40 and the comparison results output, is stored as adigital signal corresponding to the photoelectric conversion signal inthe signal storage unit 51 based upon the comparison results provided bythe comparison unit 40 and the clock signal. Through this process,12-bit digital signals are individually stored into the signal storageunit 51 and the noise storage unit 52 in the embodiment.

In addition, during the time period elapsing between the time point t11and the time point t12, the noise storage unit 52 sequentially outputs asignal, generated by time shifting the 12-bit digital signal stored inthe noise storage unit 52 by one bit at a time, to a signal line 121shown in FIG. 5 based upon a timing signal provided from the shiftregister 230. The serial signal output to the signal line 121 is inputto the demultiplexer 81. The demultiplexer 81 outputs the serial signalprovided from the noise storage unit 52 to the arithmetic operation unit80. The arithmetic operation unit 80 stores, in sequence, the digitalsignal corresponding to the noise signal into the storage unit 83. As aresult, a 12-bit digital signal corresponding to the noise signal isstored into the storage unit 83.

The signal line 121 is a signal line connecting the storage unit 50 atthe second substrate 112 with the demultiplexer 81 at the fourthsubstrate 114, which may be constituted with the through electrode 110shown in FIG. 2, bumps or the like. It is difficult to form numerousthrough electrodes 110 with a narrow pitch and, for this reason, it isdifficult to simultaneously transfer numerous parallel signals from thesecond substrate 112 to the fourth substrate 114. In the embodiment, theparallel signals stored in the storage units 50 at the second substrateare converted to serial signals and the serial signals are output to thefourth substrate 114. This means that the number of wirings connectingthe second substrate 112 with the fourth substrate 114 can be reducedand digital signals corresponding to the individual pixels 10 can besimultaneously output. Furthermore, since through electrodes 110 or thelike do not need to be formed in a great quantity, an increase in thechip area can be minimized.

During a time period elapsing between the time point t12 and a timepoint t20, the signal storage unit 51 converts the digital signalcorresponding to the photoelectric conversion signal stored in thesignal storage unit 51 to a serial signal based upon a timing signalprovided from the shift register 230 and sequentially outputs the serialsignal in correspondence to one bit at a time to the demultiplexer 81via the signal line 121. The demultiplexer 81 outputs the serial signalprovided by the signal storage unit 51 to the arithmetic operation unit80. Based upon a control signal provided by the control unit 70, thearithmetic operation unit 80 outputs the 12-bit digital signalcorresponding to the noise signal stored in the storage unit 83 to thedemultiplexer 84 in correspondence to one bit at a time. Based upon acontrol signal provided by the control unit 70, the demultiplexer 84outputs (feeds back) the digital signal corresponding to the noisesignal to the arithmetic operation unit 80.

The arithmetic operation unit 80 generates a corrected signal throughsubtraction operation executed by using the digital signal correspondingto the photoelectric conversion signal, output one bit at a time fromthe signal storage unit 51, and the digital signal corresponding to thenoise signal, output one bit at a time from the storage unit 83. Thearithmetic operation unit 80 sequentially stores the corrected signal,generated in correspondence to a single bit, into the storage unit 83.The arithmetic operation unit 80 executes the subtraction operation aplurality of times in correspondence to the number of bits in the signalstored in the storage unit 50 and sequentially stores the correctedsignal indicating the subtraction results into the storage unit 83. Inthe embodiment, 12-bit digital signals are stored in the signal storageunit 51 and the noise storage unit 52 constituting the storage unit 50,and thus, the subtraction processing is executed 12 times. Digitalsignals corresponding to the 12-bit noise signal and the correctedsignal each corresponding to one of the 12 bits are stored into thestorage unit 83. Accordingly, the storage unit 83 is constituted with 24latch circuits or the like.

In the embodiment described above, the digital CDS is executed tocalculate the difference between the digital signal corresponding to thephotoelectric conversion signal and the digital signal corresponding tothe noise signal through time division so as to determine the differencein correspondence to each bit. In addition, the arithmetic operationunits 80 are each disposed in correspondence to one of the pixels 10 andthus, the digital CDS is simultaneously executed at all the pixels 10.Since the digital CDS operation is executed in correspondence to eachbit, numerous digital circuits such as flip-flop circuits do not need tobe disposed in correspondence to multiple bits (e.g., 12 bits) at thefourth substrate 114. As a result, the number of circuits required ineach pixel 10 can be reduced, which, in turn, makes it possible toprevent an increase in the chip area.

During a time period elapsing between a time point t30 and a time pointt40, an arithmetic operation is executed in conjunction with thecorrected signals pertaining to two pixels 10 disposed in, for instance,an area A and an area B adjacent to each other in FIG. 5. Namely, the12-bit corrected signal stored in the storage unit 83 at the pixel 10disposed in the area A is input (fed back), one bit at a time, to thearithmetic operation unit 80 in the area A via the correspondingdemultiplexer 84. Likewise, the 12-bit corrected signal stored instorage unit 83 at the pixel 10 disposed in the area B is input, one bitat a time, to the arithmetic operation unit 80 in the area A via thedemultiplexer 84 in the area B, the multiplexer 85 in the area B and themultiplexer 85 in the area A. The arithmetic operation unit 80 in thearea A executes an arithmetic operation in correspondence to one bit ata time, by using the 12-bit corrected signal from the area A and the12-bit corrected signal from the area B. This operation will bedescribed in detail below.

In the operation unit 100 disposed in the area A, the arithmeticoperation unit 80 included therein outputs the 12-bit corrected signalcorresponding to the pixel 10 in the area A, stored in the storage unit83 in the area A, to the demultiplexer 84, one bit at a time. Thedemultiplexer 84 in the area A outputs (feeds back) the corrected signalto the arithmetic operation unit 80 in the area A. In addition, in theoperation unit 100 disposed in the area B, which includes the arithmeticoperation unit 80, outputs the corrected signal corresponding to thepixel 10 in the area B, which is stored in the storage unit 83 in thearea B, to the demultiplexer 84 one bit at a time. The demultiplexer 84in the area B outputs the corrected signal to the multiplexer 85 in thearea B.

A signal line 123 and a signal line 124, to which the individualoperation units 100 are connected, are connected to the multiplexer 85disposed in correspondence to each pixel 10. The signal lines 123 andthe signal lines 124 disposed in a two-dimensional pattern to extendalong the row direction and along the column direction at, for instance,the fourth substrate 114, are connected to the operation units 100 eachdisposed in correspondence to one of the pixels 10. A multiplexer 85,controlled by the corresponding control unit 70, selects a signal toundergo the arithmetic operation in the arithmetic operation unit 80from corrected signals input to the corresponding signal lines 123 and124. The multiplexer 85 in the area B outputs the corrected signalgenerated for the pixel 10 in the area B to the multiplexer 85 in thearea A via the signal line 123 shown in FIG. 5.

The multiplexer 85 in the area A outputs the corrected signal for thepixel 10 in the area B to the arithmetic operation unit 80 in the area Avia the signal line 124. The corrected signal from the pixel 10 in thearea A and the corrected signal from the pixel 10 in the area B aresequentially input, one bit at a time, to the arithmetic operation unit80 in the area A.

The arithmetic operation unit 80 in the area A generates a pixel signalthrough an arithmetic operation executed by using the corrected signaloutput one bit at a time from the storage unit 83 in the area A and thecorrected signal output one bit at a time from the storage area 83 inthe area B. The arithmetic operation unit 80 sequentially stores thepixel signal, generated in correspondence to a single bit, into thestorage unit 83. The arithmetic operation unit 80 executes thearithmetic operation a plurality of times in correspondence to thenumber of bits in each corrected signal and sequentially stores thepixel signals indicating the arithmetic operation results into thestorage unit 83. Following the arithmetic operation executed by usingthe corrected signals, the 12-bit corrected signal and a 12-bit pixelsignal will have been stored in the storage unit 83.

As described above, a corrected signal is generated in the embodimentthrough correlated double sampling executed prior to the arithmeticoperation, which is executed by using the corrected signals from theindividual pixels 10. This means that the arithmetic operation can beexecuted with the corrected signals from selected pixels 10 by firstremoving the noise signal component from the individual signals eachoriginating from one of the pixels 10. In addition, the arithmeticoperation is executed in correspondence to each bit in conjunction withthe corrected signals generated for the individual pixels 10 in theembodiment. As a result, since multiple-bit digital circuits such asmultiple-bit (e.g., 12 bit) basic mathematical operation circuits,multiple-bit (e.g., 12 bit) flip-flop circuits and the like do not needto be disposed at the fourth substrate 114, no increase in the chip areais required. Since the arithmetic operation is executed with thecorrected signals in correspondence to one bit at a time, the circuitarea of the individual arithmetic operation units 80 can be kept down.Furthermore, the arithmetic operation units 80 each execute anarithmetic operation by using corrected signals generated incorrespondence to the individual pixels 10, as well as the correlateddouble sampling. This means that the arithmetic operation unit 80functions as a correction/inter-pixel arithmetic operation unit,fulfilling the role of a correction unit that generates a correctedsignal by subtracting the value indicated in one digital signal from thevalue indicated in the other digital signal and also fulfilling the roleof an inter-pixel arithmetic operation unit that executes an arithmeticoperation with corrected signals, each generated in correspondence toone of the pixels 10. As a result, a smaller chip area is achieved incomparison to the chip area required if the correction unit and theinter-pixel arithmetic operation unit were to be disposed independentlyof each other.

The structure achieved in the embodiment includes the fourth substrate114, in addition to the third substrate 113, at which the control units70 are disposed. The arithmetic operation units 80, the multiplexers 85and the like are disposed at the fourth substrate 114. Thus, the signallines 123 and signal lines 124, disposed in a two-dimensional pattern,can be commonly connected to the operation units 100 of all the pixels10 without increasing the chip area. By outputting a control signal froma control unit 70 and controlling the corresponding arithmetic operationunit 80, multiplexer 85 and the like with the control signal, anarithmetic operation can be executed by using corrected signals fromselected pixels 10. Such an arithmetic operation can be executed withthe corrected signals from adjacent pixels or from pixels disposed inareas set apart from each other. Furthermore, the corrected signal fromanother pixel 10, to be used in the arithmetic operation executed in anoperation unit 100 is directly transmitted through a signal line 123 anda signal line 124 without going through a latch, a register or the like.Since this eliminates any time delay, which would occur when a signalpasses through a latch, a register or the like, the signal can be readout at high speed, and the arithmetic operation can be executed at highspeed in conjunction with signals from any selected pixels.

During a time period elapsing between a time point t50 and a time pointt60, the arithmetic operation unit 80 outputs the pixel signal stored inthe storage unit 83 to the demultiplexer 84. The demultiplexer 84outputs the pixel signal to the signal line 122. The sense amplifier 300amplifies the pixel signal output to the signal line 122 and reads outthe amplified pixel signal. The individual operation units 100, eachdisposed in correspondence to one of the pixels 10, sequentially outputsignals to the signal line 122, and the sense amplifier 300 sequentiallyreads out the signals output to the signal line 122.

During a time period elapsing between a time point t70 and a time pointt80, the pixel signals having been read out by the sense amplifier 300are sequentially stored into the line memory 310. The input/output unit320 executes signal processing on the signals sequentially output fromthe line memory 310 and outputs the signals resulting from the signalprocessing as image signals.

The following advantages and operations are achieved through theembodiment described above.

(1) The image sensor 3 comprises a plurality of pixels 10 each having aphotoelectric conversion unit 12 and an operation unit 100 disposed incorrespondence to each of the pixels 10, which generates a correctedsignal by using a photoelectric conversion signal output from the pixel10 and a noise signal output from the pixel 10 and executes anarithmetic operation with corrected signals each generated incorrespondence to a pixel 10. In the embodiment, prior to the arithmeticoperation executed by using the signals from the individual pixels 10, acorrected signal is generated through correlated double sampling. Thus,the arithmetic operation can be executed with the signals from selectedpixels 10 by using signals from which the noise signal component hasbeen removed in correspondence to the individual pixels 10.

(2) The operation unit 100 includes an A/D conversion unit 60 thatconverts the photoelectric conversion signal to a first digital signaland converts the noise signal to a second digital signal and acorrection/inter-pixel arithmetic operation unit (arithmetic operationunit 80) that generates a corrected signal through subtraction executedin conjunction with the first digital signal and the second digitalsignal and executes an arithmetic operation with corrected signals eachgenerated in correspondence to a specific pixel 10. This configurationmakes it possible to reduce the area taken by peripheral circuits ineach pixel, compared to the peripheral circuit area required if thecorrection unit and the inter-pixel arithmetic operation unit were to bedisposed independently of each other, and thus, the chip area can bereduced.

(3) The photoelectric conversion unit 12 is disposed at the firstsubstrate and at least part of the operation unit 100 is disposed at thesecond substrate. This structure makes it possible to prevent areduction in the opening ratio of the pixel 10.

(4) The A/D conversion unit 60 converts the photoelectric conversionsignal to the first digital signal with a first number of bits andconverts the noise signal to the second digital signal with a secondnumber of bits. Thus, digital signals obtained by individuallyconverting the photoelectric conversion signal and the noise signal canbe stored into the storage unit 50.

(5) The operation unit 100 includes a storage unit 83 where the seconddigital signal with the second number of bits is stored. The operationunit 100 executes subtraction in correspondence to one bit at a time byusing the second digital signal stored in the storage unit 83 and thefirst digital signal output from the A/D conversion unit 60. Namely, thedifferential processing in the embodiment is executed in correspondenceto one bit at a time in conjunction with the digital signal generated byconverting the photoelectric conversion signal and the digital signalgenerated by converting the noise signal. Since this eliminates the needfor disposing numerous flip-flop circuits and the like in correspondenceto each pixel 10, an increase in the chip area can be avoided.

(6) The operation unit 100 executes an arithmetic operation incorrespondence to one bit at a time by using corrected signals eachgenerated in correspondence to a pixel 10. Thus, numerous basicmathematical operations circuits, flip-flop circuits and the like thatwould otherwise be required to execute inter-pixel arithmetic operationswith signals from different pixels 10 do not need to be disposed, and asa result, an increase in the chip area can be avoided.

(7) The image sensor 3 further includes a plurality of signal lines(signal lines 123 and signal lines 124) to which the plurality ofoperation units 100 are connected and to which corrected signals areoutput from the operation unit 100. The operation units 100 each includea first selection unit (multiplexer 85) that selects corrected signalsto be used in an arithmetic operation executed at the operation unit 100from corrected signals output to a plurality of signal lines. In theembodiment, the arithmetic operation unit 80 and the multiplexer 85 arecontrolled by the control unit 70 so as to read out selected correctedsignals originating from different pixels 10. This means that anarithmetic operation can be executed by using corrected signals fromselected pixels 10.

(8) The image sensor 3 includes a pixel substrate (first substrate 111)which includes a plurality of pixels 10 each having a photoelectricconversion unit 12 that generates an electric charge throughphotoelectric conversion of light having entered therein and an outputunit 20 (readout unit 20) that generates a signal based upon theelectric charge and outputs the generated signal, and an arithmeticoperation substrate (fourth substrate 114), laminated on the pixelsubstrate that includes operation units (arithmetic operation units 80)each of which generates a corrected signal based upon a reset signalgenerated after the electric charge in the output unit 20 is reset and aphotoelectric conversion signal generated based upon the electric chargegenerated in the photoelectric conversion unit 12 and executes anarithmetic operation with corrected signals each generated incorrespondence to a pixel 10. This structure makes it possible toexecute an arithmetic operation with signals from selected pixels 10from which the noise signal component has been removed in correspondenceto the individual pixels 10. In addition, since the arithmetic operationunits 80 are each laminated on the corresponding pixel 10, the openingratio of the pixels 10 is not reduced.

(9) The image sensor 3 includes an accumulation substrate (secondsubstrate 112) that includes accumulating units (storage units 50) ineach of which a photoelectric conversion signal and a reset signalhaving been converted to digital signals are accumulated. Theaccumulation substrate is laminated at a position between the pixelsubstrate and the arithmetic operation substrate. This structureprevents the opening ratio of the pixels 10 from becoming reduced.

The following variations are also within the scope of the presentinvention, and one of the variations or a plurality of the variationsmay be adopted in combination with the embodiment described above.

(Variation 1)

In the embodiment described above, the arithmetic operation units 80 areeach used as a correction unit that executes CDS processing and also asan inter-pixel arithmetic operation unit engaged in inter-pixelarithmetic operation. However, a correction unit 54 dedicated toexecuting the CDS processing may be disposed as a unit independent ofthe arithmetic operation unit 80, as illustrated in FIG. 7. In thiscase, the arithmetic operation unit 80 simply functions as aninter-pixel arithmetic operation unit. The correction unit 54 generatesa corrected signal through subtraction executed by using the digitalsignal generated from the photoelectric conversion signal and outputfrom the signal storage unit 51 and the digital signal generated fromthe noise signal and output from the noise storage unit 52, and outputsthe corrected signal thus generated to the arithmetic operation unit 80via the demultiplexer 81.

(Variation 2)

In the embodiment described above, pixel signals resulting from theinter-pixel arithmetic operations are sequentially output to the senseamplifier 300 via the signal line 122. As an alternative, the operationunits 100 may each output the corrected signal stored in the storageunit 83 as a pixel signal to the sense amplifier 300 via the signal line122. As a further alternative, the digital signal corresponding to thephotoelectric conversion signal, stored in the signal storage unit 51,and the digital signal corresponding to the noise signal, stored in thenoise storage unit 52, may both be output to the signal line 122 via thedemultiplexer 81.

(Variation 3)

In the embodiment described above, the CDS processing and theinter-pixel arithmetic operation are both executed in correspondence toone bit at a time by allocating a time slot to each bit through timedivision. As an alternative, an arithmetic operation may be executed incorrespondence to a plurality of bits at a time by controlling thearithmetic operation unit 80 and the like through the control unit 70.For instance, the arithmetic operation may be executed in correspondenceto two bits at a time, or it may be executed in correspondence to aspecific number of bits, smaller than the number of bits in the digitalsignal stored in the noise storage unit 52, at a time.

(Variation 4)

In the embodiment described above, digital CDS is executed before thearithmetic operation is executed by using signals from individual pixels10. However, analog CDS may be executed instead before the arithmeticoperation is executed by using signals from different pixels 10. Forinstance, differential processing may be executed by using thephotoelectric conversion signal and the noise signal and then an analogsignal generated based upon the difference between the signals may beconverted to a digital signal at each A/D conversion unit 60. A digitalsignal from which the noise signal component in the particular pixel 10has been removed is stored into the storage unit 50. The digital signalstored in the storage unit 50 is then sequentially output to anarithmetic operation unit 80.

(Variation 5)

In the embodiment described above, the photoelectric conversion units 12are each constituted with a photodiode. However, a photoelectricconversion unit 12 constituted with a photoelectric conversion film maybe used, instead.

While an embodiment and variations thereof are described above, thepresent invention is in no way limited to the particulars of theseexamples. Any mode conceivable within the scope of the technicalteaching of the present invention is also within the scope of thepresent invention.

The disclosure of the following priority application is hereinincorporated by reference:

Japanese Patent Application No. 2016-60001 filed Mar. 24, 2016

REFERENCE SIGNS LIST

3 image sensor, 12 photoelectric conversion unit, 10 pixel, 40comparison unit, 60 A/D conversion unit, 100 operation unit

1. An image sensor, comprising: a pixel substrate that includes aplurality of pixels each having a photoelectric conversion unit thatgenerates an electric charge through photoelectric conversion executedon light having entered therein and an output unit that generates asignal based upon the electric charge and outputs the signal; and anarithmetic operation substrate that is laminated on the pixel substrateand includes an operation unit that generates a corrected signal byusing a reset signal generated after the electric charge in the outputunit is reset and a photoelectric conversion signal generated based uponan electric charge generated in the photoelectric conversion unit andexecutes an arithmetic operation by using corrected signals eachgenerated in correspondence to one of the pixels.